The present disclosure relates to toners including magnetic compositions for printing.
Numerous processes are within the purview of those skilled in the art for the preparation of toners. Emulsion aggregation (EA) is one such method. These toners may be formed by aggregating a colorant with a latex polymer formed by emulsion polymerization. For example, U.S. Pat. No. 5,853,943, the disclosure of which is hereby incorporated by reference in its entirety, is directed to a semi-continuous emulsion polymerization process for preparing a latex by first forming a seed polymer. Other examples of emulsion/aggregation/coalescing processes for the preparation of toners are illustrated in U.S. Pat. Nos. 5,403,693, 5,418,108, 5,364,729, and 5,346,797, the disclosures of each of which are hereby incorporated by reference in their entirety. Other processes are disclosed in U.S. Pat. Nos. 5,527,658, 5,585,215, 5,650,255, 5,650,256 and 5,501,935, the disclosures of each of which are hereby incorporated by reference in their entirety.
Magnetic printing methods employ inks or toners containing magnetic particles. Various magnetic inks and toners have been used in printing digits, characters, or artistic designs, on checks, bank notes and/or currency. The magnetic inks used for these processes may contain, for example, magnetic particles, such as magnetite in a fluid medium, and/or a magnetic coating of ferric oxide, chromium dioxide, or similar materials dispersed in a vehicle including binders and plasticizers.
Toners for Magnetic Ink Character Recognition (“MICR”) applications require a minimum magnetic remanence and retentivity to enable check reader/sorters to read the magnetically encoded text. Renanence is synonymous with retentivity and is a measure of the magnetism remaining when the magnetic particle is removed from the magnetic field, i.e., the residual magnetism. When characters printed using an ink or toner having a sufficiently high retentivity are read, the magnetic particles produce a measurable signal that can vary in proportion to the amount of material deposited on the document being generated.
Thus, a magnetic material may be added to the toner. Magnetite (iron oxide) is often used, with an acicular crystal shape. For example, U.S. Pat. Nos. 6,617,092 and 7,282,314, the entire disclosures of each of which are incorporated by reference herein, describe the use of these magnetites in the formation of MICR toners. Acicular magnetites are often 0.1×0.6 microns along the minor and major axis in size. Due to the large size of the long dimension of these particles, along with the high density of the magnetite, these particles are difficult to disperse and stabilize, and also difficult to incorporate into toner, especially in an emulsion/aggregation toner process. Thus, high levels of these magnetites may be required, which may cause difficulties in the aggregation and coalescence of an EA toner.
The magnetic material used for manufacturing such toners is highly reactive and unstable in raw form. More specifically, exposure to air may produce an exothermic reaction resulting in fires. Extra packaging requirements may thus be necessary for shipping magnetite. For example, in some cases, the size of the package may be limited or reduced. The instability of the magnetite may also prevent the materials from being transported by air, or other similar means, which require lengthy delivery times to production facilities. In addition to safety issues, the reactivity also adversely impacts magnetic properties of the material.
It would be advantageous to provide magnetic materials for forming magnetic inks and toners that provide a number of advantages, including, for example, advantageous processing of the materials, including safeguarding the magnetic materials to prevent unintended degradation thereof.